1. Field of the Invention
The present invention relates to a noise protection wall. More particularly, it relates to noise protection walls which are set up along traffic routes in order to protect wayside residential areas against the noise coming from the traffic route.
2. The Prior Art
Most noise protection walls are made from galvanized steel posts having exchangeable wall elements mounted between such posts. Certain frequencies are damped or diminished to a lesser or greater degree, depending on the construction material and the wall system. Elements which predominantly reflect the sound have a low wall cross-section and are manufactured from, for example, concrete, metal or plastic profiles. On the other hand, elements which absorb the sound for the most part have a wider structure and are composed of a porous material, for example, an open-pore expanded concrete, facing concrete, or rock wool. By means of such elements, the sound penetrates the open-pore materials and is converted into heat.
It is difficult to provide said elements with an aesthetic appearance. In most cases, such elements have a conspicuous structure and they are painted in bright colors. Such a construction with this appearance interferes with the natural scenery, and the popular discontent with such noise screens is growing, because they do not meet their visual needs.
Any after covering of the screens with plants that could hide such noise screens is often not possible due to lack of space, or due to the excessively high cost.
One possible solution is shown by the noise protection wall known from DE-OS 38 12 394, which is comprised of a framework for holding and receiving wall elements, whereby the latter consist of cassettes covered by plants, said cassettes being stacked one on top of the other for forming the height of the wall. Such a noise protection wall does not interfere with the natural scenery, but offers a successful appearance, aesthetically speaking. It offers a biotop for many microorganisms and ensures the elimination of harmful substances and good heat absorption.
With respect to sound damping or diminution values, a noise protection wall erected according to DE-OS 38 12 394 adequately meets the "Technical Specifications and Guidelines for the Design of Noise Protection Walls on Roadways" ("ZTV-Lsw 88"), which specify that the A-valued sound diminished value measured has to be reduced by at least 25 dB.
In recent times, the traffic volume on roadways and in the air has continued to grow; numerous new industrial zones with additional sources of noise have been developed, and many residential areas which only yesterday were located in a green landscape are now situated in the center of an industrial zone or near a heavily traveled road. Noise leads to an impairment of sound communication, of sleep and relaxation, and diseases of the vegetative nervous system. It is, therefore, understandable why noise is, according to a poll, perceived as being one of the severest impairments of the environment. A noise screen covered with green plants as the one known from DE-OS 38 12 394, which only offers adequate sound elimination or absorption, is no longer deemed acceptable.
With noise protection walls erected according to DE-OS 38 12 394, it is also particularly disadvantageous in that vertical tubes had to be installed later to distribute the load in order to increase the stability of the noise screen to the value required according to "ZTV-Lsw 88."